Patent GB-563666-A (GB)
Title: Improvements in or relating to automatic or semi-automatic telephone or like exchange systems
IPC: H04Q1/18
Filed: 1943-03-11
Abstract: 563,666. Automatic exchange systems. STANDARD TELEPHONES & CABLES, Ltd. (International' Standard Electric Corporation). March 11, 1943, No. 3986. [Class 40 (iv)] In a register-controller system, the method described in Specification 555,530 for the control of single-motion group selectors by the comparison of A.C. revertive signals with a selected reference current is adapted for the control of final selectors. The arrangement provides for hunting over P.B.X. groups. As the final selector, Fig. 3, passes over subnormal positions at the beginning of the successive tens groups, A.C. signals of different phase are sent over wire c to the register-controller, Figs. 1, 2, and are compared with a reference current selected by the tens register SMT. The driving circuit is opened by relay Vtr when agreement is reached and outsequence switch OM is advanced to connect up the units register SMU. If the first line of the group is required, the selector does not move, since the first position of SMU is wired back to the tens register SMT and relay Vtr immediately re-operates. Otherwise the selector advances over the group and again sends back signals of different phase for comparison with the current selected by SMU until fresh agreement causes Vtr to reoperate, these signals being of different voltage from the previous signals. Relay Vhr energizes and makes a test circuit over resistance K, relay Pbr, b wire, relay Br, wiper c, in which relay Pbr operates if the selected line is idle and connects up Sfr. The latter connects Sor in parallel with Pbr to permit the operation of switching relay Br in the final selector and grounds terminal F to bring about the completion of the connection. If the line is busy, Pbr is inoperative and relay Gbr, which follows Vhr, connects up Pcr, Sbr to ground terminal B. The first and last lines of a P.B.X. group are marked by battery through resistance R, Fig. 4. If the first line is found to be busy, relay Pcr short-circuits resistance K and Pbr then operates in series with resistance R and connects up Psr. The operation of relay Vrr releases Vtr, and the relapse of Vhr steps the units register SMU to select the reference current for the next line of the P.B.X. group, whereupon the relapse of Vrr drives the final selector to that line. If it is found busy, Gbr, Pcr pull up and reoperate Vrr to continue hunting. If the last line is busy, Pbr operates after Pcr, as when the first line is busy, and Pfr is connected up to ground terminal B. Relays Shr, Msr provide for the proper advance of the tens and units registers SMT, SMU when a P.B.X. group is contained in more than one tens group. An intermediate line (but not the last line) of a P.B.X. group may be called individually in the same way as an ordinary line. Modifications.-The tens and units controls may be effected simultaneously over separate circuits, Fig. 8 (not shown), relay Vtr being dependent on two comparison circuits. In another arrangement, Fig. 5 (not shown), the final selector as it passes over subnormal positions sends back A.C. impulses to step a counting switch until the latter reaches a position marked by the tens register SMT. In a modified arrangement for P.B.X. hunting, Figs. 6, 7 (not shown), the A.C. signals of different phase have also different frequencies (or different potentials) according as they are ordinary lines or first or last lines of P.B.X. groups. Three comparison circuits in the register-controller control individual relays Vbr to produce the various effects described above in relation to Figs. 1, 2.